This invention relates to electrical switches, and more particularly to a coaxial switch for insertion and electrical connection into a coaxial transmission line. The switch is designed to carrying high current, and to minimize the production of stray magnetic fields.
Direct current transmission systems, whether they be for superconducting machines, welding, or power distribution, generally produce large stray magnetic fields caused by the current passing through the conductors. These fields have many detrimental manifestations. One problem is that when parallel conductors are closely spaced they must normally be tightly secured to preclude the occurrence of adverse effects associated with the attraction and replusion effects produced by the magnetic fields associated with the flow of current. Another problem is the generation of stray magnetic field, which may be detrimental to other equipment; and which, when aboard ship, may be capable of enemy detection and may cause the activation of magnetic mines and/or torpedoes.
One of the best ways of eliminating or minimizing the effect of these stray magnetic fields is to transmit the current through a coaxial transmission line, which produces no external field due to the fact that the magnetic fields produced by the current in each conductor cancels that produced by the other. Where it is only desired to reverse polarity, or to merely switch the current distribution without concern for magnetic effect, prior art conventional switch-gear has been used. But such conventional switch-gear when used with a coaxial line, presents complex design problems, such as the transitional connection between the coaxial cable and the switch. The most important problem is that once the coaxial line feature is interrupted, stray magnetic fields are produced from the non-coaxial conductors within the switch and the leads thereto. Therefore in situations where such magnetic fields are detrimental, complex shielding means have to be used.
Coaxial switches in the prior art have been used for many years, particularly in radio antenna switching networks, but such switches do not usually carry high currents. In addition, one feature of this invention that is absent from practically all coaxial switches in the prior art, is the switching of current in both the inner conductor and the outer conductor or shield element. Totally non-existent in the prior art seems to be the feature of polarity reversal in coaxial switches; that is, connecting the center conductor to the shield, and connecting the shield to the center conductor when the switch is inserted between the ends of a coaxial cable.